Thermal print heads have been utilized in the past in which a row of resistive elements are driven to provide an alpha-numeric pattern on thermal print paper which is moved past the print head. In one common type print head a row of resistive elements is formed by patterned deposition on the top surface of a substrate, usually a printed circuit board. Connections to the resistive elements are made in the same plane as the top surface of the substrate, such that the print head is configured with both the resistive elements and the patterned conductors in the same plane. Since the print paper is transported immediately over the surface of the print head containing the resistive elements and printed circuit, contact to the resistive elements is somewhat difficult. Moreover, since the resistive elements are raised from the plane of the printed circuit board, there is a certain amount of wear associated with abrasion occasioned by the movement of the thermal print paper over the resistive elements. As to resolution, the resolution of the planar print head is limited by the density of the resistive elements, which is in turn, limited by the density of the interconnecting conductors or busses. Since the busses and the resistive elements occupy space in one plane, packing density is limited.
The limit to the resolution of an array of resistive elements is only partially associated with the density of the resistive elements. More importantly, the resolution is dependent upon the ability of the head to dissipate heat. While substrates have been devised which are relatively good thermal conductors, without active cooling, the resistive elements are cycled at relatively slow rates, and thus the resolution of such a planar array is limited.